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Fig. 2 Pdgfrβ regulates mural cell number, association, and development of the coronary vessels. (A,A′) Coronary vessel coverage of the ventricle. (A) Imaging of fli1a:EGFP in WT (pdgfrb+/+), heterozygous (pdgfrb+/−) and homozygous (pdgfrb−/−) fish at 98 and 167 dpf. Asterisks indicate isolated endothelial cells. (A′) Quantification of coronary vessel coverage as a percentage of the ventricle area. pdgfrb+/− fish have decreased vessel coverage at 98 dpf (∼61.8%, n=6 fish) but this recovered by 167 dpf (∼97.85%, n=4 fish). pdgfrb−/− mutants have decreased vessel coverage at both 98 dpf (∼41.45%, n=8 fish) and 167 dpf (∼40.85%, n=4 fish) compared with WT (97.76%, n=7). Error bars represent s.d. *P≤0.05, **P≤0.01 (one-way ANOVA). (B,B′) Mural cell association with different types of coronary vessels is affected differently in the pdgfrb−/− mutant. (B) Mural cell [Tg(pdgfrb:EGFP)] association with the small coronary vessels/capillaries [Tg(fli1a:DsRed)] is decreased at 100 dpf in pdgfrb−/− mutant heart. Mural cells are maintained around narrow, large (artery-like) vessels (white arrowheads), but the wider, large (vein-like) vessels (yellow arrowheads) lack mural cells. Asterisks indicate isolated endothelial cells. (B′) Quantification of mural cell recruitment on large and small coronary vessels. Mural cell number per µm vessel length on the narrow, large vessels is not significantly different between pdgfrb+/+ and pdgfrb−/−. Mural cell recruitment on the wide, large vessels and small coronary vessels is significantly decreased in pdgfrb−/− heart ventricles. n=3 vessels from each of 3-5 heart ventricles of pdgfrb+/+ and pdgfrb−/− fish. Error bars represent s.d. **P≤0.01, ***P≤0.001 (paired, two-tailed t-test). N.S., not significant (P>0.05).